A power semiconductor module provides the physical containment for several power semiconductor devices such as one or more power MOSFETs (metal-oxide-semiconductor field-effect transistors), IGBTs (insulated gate bipolar transistors), BJTs (bipolar junction transistors), thyristors, JFETs (junction field-effect transistors), diodes, etc. The power semiconductor devices are typically fabricated in one or more semiconductor dies which are attached to a power electronic substrate. A plastic housing, along with the substrate, enclose the power semiconductor devices.
Within a power semiconductor module, sufficient isolation distances between the electric potentials must be realized to ensure proper performance, safety and reliability. Due to limited space in the inner volume of a power semiconductor module, free air does not provide sufficient isolation between components under electrical voltage.
A soft potting isolation compound is often used to electrically insulate all exposed areas requiring electrical insulation. The filling height of the potting compound inside a power semiconductor module directly depends on the inner construction of the module. The need for fulfilling all other requirements as manufacturability of the plastic housing, processability and compatibility to existing production processes during manufacturing of a power semiconductor module generally results in higher filling heights of the potting compound, which adversely affects lifetime performance of the module. Thermal expansion of the potting material, for example, can cause substantial mechanical interactions between components with different thermal expansion coefficients, and even significant thermomechanical stress in the potting material itself. Under application conditions for an IGBT-based power semiconductor module, propagation of cracks in the potting material is a real concern which can lead to insulation failure of the module.
Hence, there is a need for a power semiconductor module with more reliable electrical insulation.